This dose of heparin also prevents blood coagulation in samples used for gas-exchange analyses or COP determination. However, to minimize the possible interaction of heparin with the endotoxin, we used a reduced dose of 100 U/kg/2 h IV. Assuming that the presence of heparin can block the activity of endotoxin, it may then equally affect the severity of endotoxemia in both saline solution-treated and albumin-treated endotoxemic rats. The rats were then randomly assigned to one of the following experimental groups (n = 11 in each group).
Group I (Saline Solution-Treated Rats): These control rats received three volumes of 4 mL/kg saline solution immediately after collecting data for the baseline (zero hour), and at 2 and 4 h later (a total of 12 mL/kg within a 4-h period, in addition to the 7.5 mL/kg/h saline solution that was continuously used to maintain fluid balance). This additional volume of saline solution was equivalent to a volume of 1 g/kg per dose of 25% albumin, given in the following albumin-treated groups. All variables that had been measured at baseline were measured again at 2, 4, and 6 h.
Group II (Albumin-Treated Bats): These rats were treated exactly as those in group I, but, instead of saline solution boluses, they received three doses of 1 g/kg 25% human albumin in equivalent volumes. This dose of albumin is used for improving COP in infants and children. In our preliminary trials with endotoxemia, lower doses of albumin (ie, 0.5 g/kg/h for 4 h) did not increase COP above the baseline. Therefore, we used three boluses of 1 g/kg 25% human albumin at 0, 2, and 4 h of the experiments in order to maintain a high COP level.
Group III (Endotoxin-Treated Rats): After data for the baseline levels were collected, these rats were given a single dose of 4 mg/kg endotoxin IV (Escherichia coli lipopolysaccharide; Detico Laboratories; Detroit, MI) and then were treated as in group I.
Group IV (Endotoxin-Albumin-Treated Rats): These rats were given a single dose of 4 mg/kg endotoxin as in group III, followed by three doses of albumin as in group II.